Floret Sterility Research Articles

Effects of post-anthesis heat stress on stem reserves mobilization, canopy temperature depression and floret sterility of wheat cultivars

Testing of four heat tolerant (Gourab, Sourav, Kanchan and Shatabdi) and two heat sensitive (Sonora and Kalyansona) wheat cultivars under normal and late growing post-anthesis heat stress conditions revealed higher pre-anthesis stem reserves mobilization to the final grain weight and floret sterility in heat sensitive cultivars compared to heat tolerant cultivars. The heat tolerant cultivars showed higher canopy temperature depression than the heat sensitive cultivars in both the growing conditions indicating the higher ability of heat tolerant cultivars to maintain cooler canopy environment than the heat sensitive ones.Key words: Post-anthesis; Heat stress; Floret sterility; Canopy temperature; Mobilization DOI: 10.3329/bjb.v39i1.5526Bangladesh J. Bot. 39(1): 51-55, 2010 (June)

Heat-Induced Floret Sterility of Hybrid Rice (Oryza sativa L.) Cultivars under Humid and Low Wind Conditionsin the Field of Jianghan Basin, China

Projected global warming is expected to increase the occurrence of heat-induced floret sterility (HIFS) in rice. However, there are few field-scale studies that could aid in predicting the potential risks to rice yield and developing countermeasures against yield losses. The aim of this study was to elucidate the factors that induce floret sterility under high temperature conditions during the flowering season in the field condition in China. Studies were conducted in irrigated paddy fields with the regional hybrid-rice cultivars grown in Jianghan Basin where air temperature is not so high during the flowering season but HIFS frequently occurs. The microclimate, panicle temperature, floret sterility, pollination, and size of dehiscence formed at the base of anthers were investigated. Significant losses in seed set were observed under the high temperature condition. Although the maximum atmospheric temperature was approximately 35ºC, the relative humidity was very high (around 70% at the time of maximum temperature), with low wind speeds, occasionally below 1 m s1. Under such conditions sunlit panicle temperature exceeded atmospheric temperature by as much as 4ºC. Moreover, the anthers of some cultivars exhibited short basal dehiscence, and the dehiscence length was positively correlated with the percentage of sufficiently pollinated florets (r=0.859, P<0.05, n=7) and with seed set (r=0.827, P<0.05, n=7) across the cultivars. The results suggest that the combination of hot, humid, and windless climatic conditions with short basal dehiscence of anthers induces HIFS in hybrid rice grown in this region.

Floret Sterility Induced by High Temperatures at the Flowering Stage in Rice (Oryza sativa L.)

地球の温暖化に伴い，高温によるイネの不稔の発生頻度が増すのではないかと懸念されている．温暖化が高温不稔を通じてイネの収量に及ぼす影響を明確にすること，それに対する対策をその効果と共に示すことは，作物学分野の重要な課題である．この総説は，主に開花期の高温によるイネの不稔発生を対象とした．まず，開花期の高温による不稔の発生条件に関連するこれまでの報告を整理した．次に，高温不稔の発生の仕組みに関する研究について解説し，最後に，耐性品種の育種を中心とした対策技術の創出において重要な，高温不稔に対する耐性に関する研究の現状について解説した．

Possible correlation between high temperature-induced floret sterility and endogenous levels of IAA, GAs and ABA in rice (Oryza sativa L.)

In order to explore the possible physiological mechanism of high temperature induced sterility in rice, we examined the floret sterility and endogenous plant growth regulator contents in pollens of two hybrid rice cultivars Shanyou63 and Teyou559 that are tolerant and susceptible to high temperature, respectively. Indexes of floret sterility, pollen activity, and variation of endogenous indole-3-acetic acid (IAA), gibberellic acids (GAs), abscisic acid (ABA), free proline and soluble proteins in anthers were measured. We found that during the course of high temperature treatment, both cultivars exhibited a marked decrease in pollen activity, pollen germination and floret fertility; however, the high temperature tolerant Shanyou63 showed a much slower rate of decrease than the high temperature susceptible Teyou559. In addition, anthers of both cultivars displayed a decrease in the contents of IAA, GAs, free proline and soluble proteins but an increase in the ABA content. Yet compared to Teyou559, Shanyou63 retained significantly higher levels of free praline and GAs and a lower level of ABA, along with higher pollen vigour and pollen germination rate even after prolonged high temperature treatment. Our study suggests a possible correlation between pollen viability/floret sterility and high temperature-caused changes in IAA, GAs, ABA, free proline and soluble protein contents. The severity in these changes may reflect the variation of rice cultivars in their heat stress sensitivities for floret development.

Stability of Rice Pollination in The Field Under Hot And Dry Conditions in The Riverina Region of New South Wales, Australia

Even Under Extremely Hot (40ºC) Conditions During Anthesis, Heat-induced Floret Sterility Does Not Appear To Be A Serious Issue For Australian Rice Growers. This Contradicts Previously Reported Temperature Thresholds For Floret Sterility. To Determine The Factors Associated With Stable Rice Production Under Hot and Dry Conditions in The Riverina Region of New South Wales (Australia), We Examined Rice (Cv. ‘Langi’) Pollination At Different Distances From The Windward Edge of A Paddy Field and Its Association With Canopy Microclimate. With An Air Temperature of 34.5ºC and A Relative Humidity of 20.7% During Anthesis, Poor Pollination of Florets Occurred At The Windward Edge, But Pollination Remained Stable Farther From The Edge. The Temperature Difference Between The Air and The Panicles in The Canopy Reached As High As 6.8ºC Under These Conditions Because of Low Humidity and Strong Transpirational Cooling. Moreover, The Length of The Dehiscence At The Base of The Thecae During Anthesis Was Long; This Is A Desirable Trait For Heat Tolerance. The Long Basal Dehiscence of The Thecae of This Cultivar and The Lower Panicle Temperatures Relative To The Ambient Temperature Caused By High Transpirational Cooling Appear To Be The Key Factors Responsible For Stable Pollination Under The Extremely High Temperatures of The Riverina Region.

Ethyloxanilates as specific male gametocides for wheat (Triticum aestivum L.)

AbstractInduction of male sterility by deployment of male gametocides holds immense potential in heterosis breeding of wheat. The efficacy of a new class of male gametocide for wheat (Triticum aestivum L.) is described: ethyloxanilates, the most active example of this class being ethyl 4‐fluorooxanilate (E4FO). E4FO induces male sterility, specifically, without detectable effects on various agronomic features and female fertility. The plants sprayed once with 0.15% E4FO exhibited 100% pollen and floret sterility without causing a significant reduction in total yield. E4FO was screened on 29 genotypes of wheat at 0.15% test concentration and was observed to induce 99.76 ± 0.37% male sterility. Thirteen F1‐hybrids of wheat were produced using the gametocide in Winter 2000–2001 and were evaluated for their agronomic performance in Winter 2001–2002. The cross combinations viz., lines WR 544 × HW 2046 and HW 2044 × WR 956 have outperformed their respective better parents by 48.17% and 23.42% in grain yield/plant and thus have potential as hybrids.

Nitrogen fertiliser alleviates the disorder straighthead in Australian rice

Straighthead is a ‘physiological’ disorder of rice, the symptoms being floret sterility, deformed florets and panicles and reduced grain yield. Straighthead in rice is difficult to investigate because of its unpredictable occurrence under field conditions. An experiment was conducted in south-eastern Australia in 1996 to investigate the effect of rate and timing of N fertilisation on growth and yield of rice. The presence of straighthead at this location gave a unique opportunity to study the influence of crop N status. This paper reports the influence of N application on straighthead symptoms during this experiment. A significant reduction of straighthead occurred with higher rates of N application. Application of 250 kg N/ha pre-flood, improved plant growth and vigour with subsequent increased uptake and accumulation of S, P, K, Mg, Cu, Mn and Zn in the plant at panicle initiation. The reduction of straighthead at high nitrogen rates may be due to improved uptake of several essential nutrients, and Cu may be a critical nutrient. This study and earlier observations have shown the application of optimal levels of pre-flood nitrogen to achieve grain yields greater than 10 t/ha may reduce straighthead severity in the Australian rice-growing environment. The results in this paper are not presented as recommendations to growers but a contribution to the currently limited literature on straighthead in Australia.

Correlation between Viability of Pollination and Length of Basal Dehiscence of the Theca in Rice undera Hot-and-Humid Condition

Anticipated global warming may increase the floret sterility of rice (Oryza sativa L.). For selection of genotypes tolerant to high temperatures during the flowering period, it is important to identify morphological traits associated with tolerance to temperature stress. This study investigated the relationship between the length of dehiscence at the basal part of thecae and the viability of pollination in 18 cultivars of rice subjected to a hot-and-humid condition (37/25 ˚C, day/night, >90% relative humidity) for three days at flowering. Control plants were left under the ambient conditions in a semi-cylindrical house covered with cheesecloth (30% shading; temperature range: 24-35 ˚C). The length of basal dehiscence of thecae and the number of pollen grains on the stigmata were examined with a light microscope after flowering. The length strongly correlated with the percentage of florets having more than 80 pollen grains on the stigmata under the ambient condition (r = 0.72, P < 0.001), and with the percentage of florets having more than 20 pollen grains on the stigmata under the hot condition (r = 0.93, P < 0.001). In other words, the length correlated with pollination viability or reliability under both conditions. In addition, basal dehiscence was shorter in the non-japonica-type cultivars than in many of the japonica-type cultivars under both conditions. We concluded that the low pollination viability in the non-japonica-type cultivars is associated with their small basal dehiscence on the thecae, and the length of basal dehiscence can be used as a selection marker of high temperature tolerance.

QTL mapping of chromosomal regions conferring reproductive frost tolerance in barley ( Hordeum vulgare L.).

Spring radiation frost is a major abiotic stress in southern Australia, reducing yield potential and grain quality of barley by damaging sensitive reproductive organs in the latter stages of development. Field-based screening methods were developed, and genetic variation for reproductive frost tolerance was identified. Mapping populations that were segregating for reproductive frost tolerance were screened and significant QTL identified. QTL on chromosome 2HL were identified for frost-induced floret sterility in two different populations at the same genomic location. This QTL was not associated with previously reported developmental or stress-response loci. QTL on chromosome 5HL were identified for frost-induced floret sterility and frost-induced grain damage in all three of the populations studied. The locations of QTL were coincident with previously reported vegetative frost tolerance loci close to the vrn- H1 locus. This locus on chromosome 5HL has now been associated with response to cold stress at both vegetative and reproductive developmental stages in barley. This study will allow reproductive frost tolerance to be seriously pursued as a breeding objective by facilitating a change from difficult phenotypic selection to high-throughput genotypic selection.

Rice is more sensitive to salinity than previously thought

Field studies conducted by UC and under controlled greenhouse conditions by the U.S. Department of Agriculture's Agricultural Research Service indicate that rice is more sensitive to salinity than current guidelines suggest. This information is particularly important to rice growers who have experienced salinity problems after holding water on fields for longer time periods to reduce pesticide loading into the Sacramento River. Our field experiments show that an average seasonal salinity of the field water in excess of 1.9 deciSiemens per meter (dS/m) can reduce grain yields; current guidelines indicate that salinity affects rice yield at or above 3.0 dS/m. Salinity had a negative impact on a number of yield components including stand establishment; panicles, tillers and spikelets per plant; floret sterility; individual grain size; and even delayed heading. The emergence and early seedling growth stages were most sensitive to salinity, as was the three-leaf to panicle-initiation stages. Irrigation management practices should be adopted to minimize salinity during these critical growth stages.

Mechanism of Anther Dehiscence and Floret Sterility Induced by High Temperature at Flowering in Rice

Mechanism of Anther Dehiscence and Floret Sterility Induced by High Temperature at Flowering in Rice

The Difference in Sterility due to High Temperatures during the Flowering Period among Japonica-Rice Varieties

SummaryThe objectives of this study are to compare the floret sterility induced by a high temperature given in the daytime during the flowering period among nine japonica rice varieties, and to clarify the mechanism of the high-temperature-induced sterility. Nine japonica rice varieties were subjected to 35.0, 37.5 or 40.0°C day- temperature conditions (1000-1600) for six consecutive days using sun-lit phytotrons, and the percentage of fertility, pollination and germinated pollen grains on the stigmas were examined. The temperature that caused 50% sterility varied with the variety, and a difference of approximately 3.0°C was observed between the most tolerant and susceptible varieties. Under the 37.5°C day-temperature condition, the percentage of florets with 10 or more germinated pollen grains was roughly coincident with the percent fertility, but under the 40° C day-temperature condition, it was higher than the percent fertility. Many of the florets with less than 10 germinated pollen grains had less than 20 total pollen grains on their stigmas under both temperature conditions. From these results, we concluded that sure pollination under high-temperature conditions is an important factor and that the high-temperature tolerance of the processes following pollen germination is also required for fertility under excessively high temperature conditions.

Comparison between Anthers of two Rice (Oryza saliva L.) Cultivars with Tolerance to High Temperatures at Flowering or Susceptibility

Anthers of rice cultivar, cv. Nipponbare, which showed floret fertility even when the temperature at flowering was high(tolerant) and cv. Hinohikari, which showed floret sterility at high temperatures (susceptible) were compared. The anther of Nipponbare had better developed cavities for dehiscence and thicker locule walls than Hinohikari. The well-developed cavities enable easy rupture of the septa in response to swelling of the pollen grains. The thick locule walls promote the swelling of pollen grains by retaining water in the locules. Since the swelling of pollen grains is the driving force to open the theca and the septum rupture is an indispensable process for the theca dehiscence, the well-developed cavities and the thick locule walls may be responsible for the tolerance to high temperatures in Nipponbare.

High Temperature at Flowering Inhibits Swelling of Pollen Grains, a Driving Force for Thecae Dehiscence in Rice (Oryza sativa L.)

SummaryTo clarify the mechanism of high temperature-induced floret sterility in rice (Oryza sativa L.), we studied the effects of high temperature at flowering on the ability of thecae to dehisce and on pollen-grain swelling which causes thecae dehiscence. Two japonica rice cultivars, grown in four L pots under submerged soil conditions were subjected to high (39°C) and moderate (34°C) temperatures from 10 : 00 to 16 : 00 for three consecutive days at the flowering stage. The percentage of the thecae dehisced in response to artificial opening of the florets by removing lemma and the mean diameter of the pollen grains measured during four minutes after the artificial opening were examined to determine the ability of the thecae to dehisce and that of the pollen grains to swell, respectively. The high temperature given on the day of flowering decreased both the percentage of the dehisced thecae and the diameter of the pollen grains but did not affect the relationship between them. The thecae of the plants which had been subjected to the high temperature for one or two days before flowering, however, showed a lower dehiscence percentage than those of the plant treated on the day of flowering against the same pollen-grain diameter. We concluded that high temperature given on the day of flowering decreased the ability of the pollen grains to swell resulting in poor thecae dehiscence, and that, besides this decrease, high temperature given just before the days of flowering lowered the function of thecae themselves to dehisce, causing poorer thecae dehiscence.

Effects of pre-anthesis moisture stress on floret sterility in some semi-dwarf and conventional height spring wheat cultivars

This study was conducted to investigate the response of some semi-dwarf Canada Prairie Spring wheat (Triticum aestivum) and conventional height (tall) cultivars of Canada Western Red Spring wheat to moisture stress at the booting stage. The effect on the frequency of sterile florets was determined in the two height groups. Drought tolerance was investigated using the electrolyte leakage test. The association of floret sterility with pollen viability under moisture stress conditions was also investigated. When fully watered, several of the semidwarf cultivars had a lower frequency of sterile florets compared with the tall cultivars. Moisture stress increased the frequency of sterile florets in both semi-dwarf and tall wheat cultivars. As moisture stress increased, the resulting sterility was significantly higher in semidwarf cultivars, relative to the tall cultivars (P ≤ 0.01). Comparisons between floret sterility and desiccation injury (estimated by electrolyte leakage tests) suggest that a high degree of floret sterility was not associated with lower levels of desiccation tolerance. Cultivar differences in pollen fertility and for electrolyte leakage in response to moisture stress were evident, but were distributed independently of height class. Key words: Wheat cultivars, moisture stress, floret sterility, pollen sterility

Floret sterility and outcrossing in two spring wheat cultivars

A tendency for higher outcrossing potential in Canadian semidwarf wheat (Triticum aestivum L.) cultivars compared with tall Canadian cultivars has been postulated by breeders and seed growers. In the present study, the outcrossing potential of a semidwarf Canada Prairie Spring wheat (Triticum aestivum L.) cv. Cutler and a conventional height Canada Western Red Spring wheat, cv. Roblin was determined under controlled greenhouse conditions. Outcrossing of each cultivar was induced by applying moisture stress followed by exposure to pollen from a phenotypic marker stock, cv. P8901. In the controlled absence of external pollen, moisture stress significantly reduced seed set in both cultivars. Application of external pollen following moisture stress increased seed set significantly in Cutler and nonsignificantly in Roblin, and was associated with a higher level of floret opening in Cutler. Outcrossing frequency was also assessed by analysing progeny seed (selfed or outcrossed) using acidic polyacrylamide gel electrophoresis of seed protein, RAPD markers and morphological phenotype, including height, awnedness, black chaff and time to maturity. All three assay techniques demonstrated a higher outcrossing frequency in Cutler than in Roblin under this protocol. The frequency of outcrossing in different parts of the spike was also determined for both cultivars. In both cultivars the highest proportion of outcrossing was found in the mid-upper region of the spike, followed by the mid-lower region. Key words: Floret sterility, moisture stress, outcrossing, Triticum aestivum

Heritability and Genotype × Environment Interactions for Straighthead in Rice

Straighthead is a physiological disorder of rice (Oryza sativa L.), which is manifested by floret sterility resulting in yield loss. The objectives of this study were to estimate the narrow‐sense beritability (h2) and the relative importance of genotype × environment interactions for straighthead and to suggest an optimum experimental design for straighthead screening. Ten commercial cultivars and 22 randomly chosen experimental lines representing southern USA rice germplasm were tested from 1991 to 1993 at three Arkansas locations: Stuttgart [Crowley silt loam (fine, montmorillonitic, thermic Typic Albaqualf)], Marianna (Loring silt loam [fine‐silty, mixed, thermic Typic Fragiudalf)], and Colt [Calloway silt loam (fine‐silty, mixed, thermic Glossaquic Fragiudalf)]. Straighthead was induced by monosodiumm ethane arsenate [4.48 kg a.i. ha−1] incorporated into the soil before planting combined with a permanentf lood established at the five‐leaf stage and maintained at each location. The genotype × year and the genotype × location interaction variance components were near zero. The three‐way interaction was significant, but its variance component was one‐fourth the magnitude of the genetic variance. The nature of the genotype × environment interaction was explored by determining the number of significant crossover (rank change) interactions. There were 798 significant crossover interactions or 4.5% of the possible 17 856 quadruples. Thus, genotype × environment interactions were minor and due primarily to changes in magnitude rather than to changes in rank. Heritability (single plot basis) was 61%, indicating that selection for resistance to straighthead should be relatively easy in southern U.S. rice germplasm. Two locations with four replications per location should be adequate for screening southern U.S. rice germplasm for reaction to straighthead.

Management strategies for maintaining rice yield within rice-based cropping systems

A five-year study was undertaken to develop management strategies for maintaining yield of consecutive annual rice (Oryza sativa L.) crops. Stubble management technique, N application rate and N application time were all important determinants of yield; together they accounted for up to 80% of yield variance. Incorporating stubble, rather than burning it, had little initial effect on yield but, from the third crop onwards, stubble-incorporation plots out-yielded stubble-burn plots by an average 0.35 t ha−1 per crop. The higher yield was due to an average 11% increase in panicle number. Yield of unfertilized rice fell from 9 t ha−1 to 3.7 between the first and fifth crops, with much of the fall occurring between the first two crops. The highest-yielding treatment in the fourth crop (which received 105 kg N ha−1 at permanent flood (PF) plus 105 kg N ha−1 at panicle intiation (PI)_did not achieve the yield of the first rice crop receiving 50 kg N ha−1 at PF (8.3 t ha− compared with 9.6). This suggests that N applications in excess of 200 kg N ha−1 were necessary to maintain yield. Fertilizing at sowing had little effect on yield. However, fertilization with a five-year average of 94 kg N ha−1 prior to PF resulted in higher average yield (6.8 t ha−1) than that obtained from plots receiving all their fertilizer at PI (6.1 t ha−1). The difference between PF- and PI-fertilized plots became greater with increasing number of crops and was because of increased floret sterility in crops receiving all their N at PI. It was concluded that reasonable yield of annual rice crops could be maintained with a combination of stubble incorporation during autumn-winter plus relatively heavy N applications just prior to PF.

The growth and nitrogen economy of rice under sprinkler and flood irrigation in South East Australia

The agronomic implications of growing rice under sprinkler irrigation on a duplex soil in inland south east Australia were examined by comparing 3 sprinkler irrigation regimes applied once, twice and three times a week (S1W, S2W and S3W) with continuous flood irrigation (CF). Each sprinkler irrigation treatment was managed to replace evaporative loss since the previous irrigation. Each irrigation main plot was split into subplots receiving 3 levels of nitrogen (N) fertilizer −0, 80 or 120 kg N ha−1 (0N, 80N and 120N). Grain yield on all sprinkler-irrigated treatments was reduced by 50% or more when compared with CF. There was a slight decline in grain yield with lower frequency of sprinkler irrigation. The main factors contributing to the lower yields were reductions in the number of spikelets per panicle and in floret fertility. Panicle density was not significantly influenced by the irrigation treatments. Sprinkler irrigation delayed anthesis by at least 8 days, and the duration of anthesis was extended by 5 to 7 days. The lower yields under sprinkler irrigation did not appear to be due to greater N deficiency and it is uncertain whether any or all irrigation treatments suffered from P deficiency. Irrigation treatment had little effect on plant N concentration, but P concentration in the plant tops was reduced by sprinkler irrigation during the vegetative and reproductive stages. Low night temperatures throughout the reproductive phase reduced floret fertility, but all irrigation treatments at the same N rate (except SlW/120N) were affected to a similar extent. Water stress, as evidenced by leaf rolling in response to high evapotranspiration rates in this semi-arid environment, was considered to be the main factor contributing to the decline in yield on the sprinkler-irrigated treatments. The irrigation and N rate treatments did not interact significantly in their effect on any important parameter measured. Increasing the rate of applied N from 0 to 80 kg N ha−1 increased yield by about 1 t ha−1 by producing more panicles, but 120N was of no further benefit and was associated with increased floret sterility. Nitrogen fertilizer increased both the N uptake and N concentration in the plant material. We conclude that sprinkler irrigation for rice production is unlikely to be a viable strategy for water management on duplex soils in inland south east Australia. Conventional dry-seeded culture with permanent flood delayed until panicle initiation is probably a preferable alternative to sprinkler irrigation for increasing water-use efficiency.

High-temperature-tolerant wheat: A description of variation and a search for some limitations to productivity

Abstract The hypothesis was examined that rapid phenology, poor biomass production and sterility are major factors leading to the poor yields of wheat grown from sowing to maturity at high temperatures. Twenty-four genotypes which were chosen for their differences in growth and floral development at moderate temperatures were compared in a glasshouse study of minicanopies planted and grown at 30/25°C, and exposed to high radiation, long days, and near-optimal water and nutrient availability. Absolute differences among genotypes in growth and floral development became small at these high temperatures, with most genotypes reaching floral initiation by 2 weeks after sowing and anthesis by 50 days. However, a short vegetative period did not prevent rapid rates of biomass production (which averaged 22 g m −2 during tillering) and the emergence of at least six ears per plant. Furthermore, there was little evidence that high temperature resulted in floret sterility except in two of the genotypes and consequently harvest index was generally very high. The range in grain yields among genotypes was 0–10 g plant −1 which converts to 0–800 g m −2 ; more than 70% of genotypes bettered 7 g plant −1 . It is suggested that ‘high-temperature-tolerance’ already exists in many common wheats. A major boost to yields in countries with a hot start to the season would come with the appreciation that the potential of the crop is very largely set in the first 2–3 weeks after sowing, during which all aspects of agronomy must be optimized. Failure to do this could account for a reduction in potential yields from 6 down to less than 1 t ha −1 . Factors in this period likely to affect potential yield are discussed.